The proposed project will investigate the effects of neonatal undernutrition on norepinephrine (NE), dopamine (DA), and serotonin (5HT) biochemical mechanisms in the rat. Undernutrition will be induced (1) Preweaning, by feeding a low protein diet to lactating females and (2) Postweaning, by feeding a low protein diet for three additional weeks. Animals will then be nutritionally rehabilitated on a 25% casein diet. Development of central neurotransmitter systems will be monitored by measurement of regional development of endogenous NE, DA, and 5HT levels, Tyrosin hydroxlase (TH), Dopamine-beta-hydroxylase (DBH), and tryptophan hydroxylase activity. The synthesis of NE, DA from tyrosine and 5HT from tyrosine will also be assessed. Parallel studies will be carried out in the peripheral nervous system: adrenal, superior cervical ganglia, and mesenteric artery. All biochemical determinations will be carried out from birth to adulthood, during periods of undernutrition as well as after nutritional rehabilitation. The adult response to stress (foot shock, swimming) will be studied by assessing the rates of NE, DA, and 5HT synthesis. Preliminary data suggest that rats malnourished early in life exhibit hyperresponsivity to stressors as adults. These studies should elucidate some of the neuronal mechanisms operative in animals underfed during early growth and development.